Andreas Gal, an engineer who helped speed up the Firefox browser at a crucial moment and then helped launch the Firefox OS project, has been promoted to Mozilla's new chief technology officer.

"Andreas is widely recognized as an authority on web technology and as a strong technical leader," said Chris Beard, Mozilla's acting chief executive, in a blog post Thursday. "He will also continue to serve as VP Mobile as we continue to focus our efforts on delivering and scaling Firefox OS."

Gal replaces Brendan Eich, a Mozilla co-founder who was named CTO in 2005 but then resigned from the nonprofit organization after a tumultuous 11-day stint as CEO. Gal will have big shoes to fill: despite Eich's resignation, triggered by a controversy stemming from his 2008 donation to a cause opposing gay marriage in California, Eich is the inventor of the JavaScript programming language and a respected leader in Web technology.

"For me, the open Web is a unique ecosystem because no one controls or owns it...Every browser vendor can prototype new technologies for the Web. Once Mozilla led the way with Firefox, market pressures and open standards quickly forced competitors to implement successful technology as well. The result has been an unprecedented pace of innovation that has already displaced competing proprietary technology ecosystems on the desktop," Gal said. "We are on the cusp of the same open Web revolution happening in mobile as well, and Mozilla's goal is to accelerate the advance of mobile by tirelessly pushing the boundaries of what's possible with the Web."

Gal's appointment means continuity for Mozilla during a period of dramatic, highly public disagreement. He worked closely with Eich, the very person who recruited Gal to Mozilla six years ago.

At the time, Gal had been working at the University of California-Irvine on an idea unusual for academia but very important for browsers, a way to accelerate JavaScript -- the language that transforms Web pages from static documents into interactive sites and nowadays apps. Faster JavaScript has helped make the Web more polished and elaborate, opening the door for online apps such as Google Docs.

Gal did a lot more, though, and rose through the ranks to become vice president of Mozilla's all-important mobile efforts, which include Firefox for Android and the Firefox OS operating system project that Gal co-founded. Both of those compete against better established software from market leaders Apple and Google.

"What we're focused on now is not to take on iOS or even Android," Gal told CNET earlier this month. "Seventeen percent of the market has a smartphone. It's the other 83 percent who have some kind of flip phone or feature phone. We're going to a huge market where people are yearning to have their first smartphone experience."

Today's browsers are architecturally all very similar, but Servo is an attempt to start fresh with a design tailored for modern computing devices whose multicore processors can handle many tasks in parallel.

Today's browser architecture was "designed when most devices had a single core. Today's cell phones are headed for eight cores and more. There's a fundamental design disconnect between browser design and where the technology is headed."

JavaScript gives life to Web pages, but it's also been steadily making Web pages bulkier and therefore slower to download, according to HTTP Archive statistics from hundreds of thousands of Web pages.Photo by HTTP Archive

As CTO, Gal also will have to wrestle technology issues beyond Mozilla's walls, too. Almost uniquely in the computing industry, browser makers are reliant on cooperation with the closest competitors. That's because new features offer Web programmers more power, but those programmers aren't likely to support the features unless other browsers also support it.

Nobody wants to go back to the bad old days when Microsoft's Internet Explorer was almost the only browser used and Web pages often worked badly or not at all with other browsers. At the same time Mozilla develops its own standards, it evaluates which from other browser makers are important to support or sufficiently problematic that Mozilla should reject them. Much of that discussion takes place within standards groups -- including ECMA's TC39, which oversees JavaScript, and where Eich has been a central figure.

Gal is fluent in JavaScript issues. When he joined Mozilla, academics were focused chiefly on traditional programming languages that are compiled in advance into the machine code computers actually execute, but that's not how JavaScript code works.

Instead, JavaScript downloaded along with the rest of a Web page and run on the spot. That tends to make software run slower than natively compiled software, but browser makers have been dramatically speeding up JavaScript with a variety of approaches. Core to the work has been something called just-in-time (JIT) compilation, which creates a native version of the JavaScript as soon as the browser starts running it.

JIT compilation can take a long time, though, and people want their Web pages to work immediately. Gal led a project called TraceMonkey that watched what parts of a JavaScript program was most active and compiled that.

"Three months before the release of Chrome, we had the first public release of TraceMonkey," Gal said. "The performance wars started right after that. That was the starting point of my career at Mozilla."

TraceMonkey arrived in Firefox 3.1 just before Google changed the browser game by announcing Chrome in 2008. Unfortunately for Mozilla, TraceMonkey wasn't fast enough in all circumstances, but it adopted some Google's software directly from Chrome with a new JavaScript engine called JaegerMonkey that arrived in Firefox 4. Next up was Firefox's more refined approach, IonMonkey, which brought another speed boost.

The gradually improving JavaScript performance has let Mozilla use it to tackle parts of the Web that before needed plug-in software. For example, its pdf.js replaces Adobe Reader and its newer Shumway is designed to replace Adobe's Flash Player. Gal was involved in both projects. And one of the highest-profile projects at Mozilla today, asm.js, seeks to radically improve JavaScript performance for programmers who want to convert native apps written in C or C++ to the Web.